Apparatus for continuous casting of directionally solidified articles

ABSTRACT

Apparatus for continuous casting of directionally solidified articles in which the cooperating mold elements are heated, moved into cooperating relation to one another, filled and cooled for solidifying the alloy after which the mold elements are separated for removal of the cast alloy from the mold.

United States Patent [191 Waring [451 Nov. 13, 1973 APPARATUS FOR CONTINUOUS CASTING OF DIRECTIONALLY SOLIDIFIED ARTICLES [75] Inventor: Dana B. Waring, Glastonbury,

Conn.

[73] Assignee: United Aircraft Corporation, East Hartford, Conn.

221 Filed: Feb. 22, 1972 21 Appl. No.: 227,837

[52] US. Cl. 164/279, 164/60, 164/82,

164/130' [51] Int. Cl 822d 11/06, 822d 25/06 [58] Field of Search 164/60, 122, 125, 164/127, 130, 158, 279, 82, 89

[56] References Cited UNITED STATES PATENTS 3,281,903 11/1966 Ross 164/279 X 2,804,664 9/1957 Brennan.... 164/130 X 3,170,205 2/1965 Brown 164/60 1,961,399 6/1934 Snook 164/82 FOREIGN PATENTS OR APPLICATIONS 734,347 7/1955 Great Britain 164/279 1,057,291 5/1959 Germany 748,643 5/1956 Great Britain 164/130 OTHER PUBLICATIONS Process Speeds Up Directional solidification, Erickson et al., Metal Progress, 3/1971, pp. 58-60.

Primary ExaminerRobert D. Baldwin Assistant Examiner.1ohn E. Roethel Att0rneyCharles A. Warren [5 7 ABSTRACT Apparatus for continuous casting of directionally solidified articles in which the cooperating mold elements are heated, moved into cooperating relation to one another, filled and cooled for solidifying the alloy after which the mold elements are separated for removal of the cast alloy from the mold.

12 Claims, 6 Drawing Figures Patented Nov. 13, 1973 2 Sheets-Sheet 1 Patented Nov. 13,1973 3,771,586

2 Sheets-Sheet 2 APPARATUS FOR CONTINUOUS CASTING OF DIRECTIONALLY SOLIDIFIED ARTICLES BACKGROUND OF THE INVENTION Because of the nature of most alloys cast in directionally solidified form, such casting is done in a vacuum or in an inert atmosphere, thus necessitating a closed chamber in which the desired atmosphere may be maintained and in which the casting takes place. Each casting operation thus requires opening the chamber either directly or through air locks for the removal of a filled and solidified mold and the replacement with an empty mold to be filled and solidified. Such opening of the chamber and the reestablishment of the desired atmosphere is time consuming and thus the total elapsed time for the casting operation is relatively long.

STATEMENT OF THE INVENTION One of the principal features of the invention is a machine for making directionally solidified articles of the columnar grained type of VerSnyder U.S. Pat. No. 3,260,505 or the single crystal type of Piearcey U.S. Pat. No. 3,494,709. The term columnar grained is intended to include both of these types as the single crystal is in fact one form of columnar grain material in a continuous process capable of operating continuously within a vacuum or an inert gas chamber. Another feature is the accomplishment of the mold heating and cooling together with the initiation. of grain growth in directionally solidified form in a continuous process in forming directionally solidified cast articles.

According to the invention, the apparatus includes conveyor means for carrying a series of mating mold elements past a heating means into cooperating relationship with each other, means for successively filling the cavities in the cooperating set of mold elements, means for initiating and continuing the directional solidification of the material in the mold cavities and means for separating the cooperating mold elements for the removal of the cast articles therefrom. The process involves the steps of heating mold segments of a series of article molds successively, positioning the mating segments in juxtaposition to define a casting cavity in each set of mating parts, successively filling the cavities in said series of molds, directionally solidifying the alloy in the mold cavities to form the cast articles and separating the mating mold parts for removal of the cast articles from the molds.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical sectional view through a vacuum DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing, the apparatus is shown as positioned within a vacuum chamber 2 so that the casting process or the operation of the apparatus may take place within a protective atmosphere such as a vacuum or an inert gas atmosphere. The alloy to be cast is supplied in the form of a bar 4 which enters the vacuum chamber through a seal 6 in the bottom thereof and the bar is enclosed within a tube 8 which at the top is re fractory and serves as a melting pot 10 for the alloy with a pouring spout 12 through which the molten alloy is directed to a filling device 14 in the form substantially of a funnel having a discharge spout or opening 16. The expression vacuum chamber obviously refers to a chamber in which either a vacuum or other protective atmosphere may be established and maintained.

The bar 4 of alloy material is supplied at such a rate that the level of the pool of molten alloy at the top thereof remains as substantially the same level at all times. A suitable control means for the feed of this bar and a control of the height of the upper end thereof is described by way of example in the Elam U.S. Pat. No. 3,590,777. This patent has a device for sensing the level of the molten surface and for energizing feeding means for maintaining that level.

A suitable device is provided for melting the bar as it is advanced into the pot at the upper end of the refractory tube. In the arrangement shown, the heating means is an electron beam heat source 18 with the beam directed on to the top end of the bar of alloy through a tube 20 positioned at the top of the chamber. The selection of the electron beam heat source is not critical and other suitable types of heating means may be utilized in the same manner.

The alloy is cast in a succession of molds 24, each mold consisting of opposed segments 24a and 24b which when placed in contact with one another, form a cavity therein in which the article is cast. The successsive molds 24 are in endwise engagement with one another during the time that they are being filled and that the alloy therein is solidifying so that a continuous flow of .molten material may be supplied to these molds without the loss of alloy between adjacent molds.

For supporting the molds in the desired position for casting, all of the mold segments-24a are mounted on a conveyor belt 26 and the mold segments 24b are mounted on a conveyor belt 28. These belts are positioned vertically in the vacuum chamber and in parallel relation to one another. Cooperating rolls 30 atjthe top of the belts and other rolls 32 at the bottom of the belts support them in proper spaced relation to one another. The mold segments move over the rolls 30 and downward into juxtaposition with one another between the rolls 30 and are held in contact with each other to a point between the lower cooperating rolls 32. At this point as the belts move around the rolls 32, the mold segments are separated from one another and the cast articles are released therefrom. The successive mold segments are also moved into vertical contact one with another at the rolls 30 so that the successive molds form a continuous casting cavity all the way from a point adjacent the plane of the center lines of the rolls 32 for the conveyor belts to a point adjacent the plane of the center lines of the top rolls 30. The spout 16 is located directly above the point where the mold segments come together so that a continuous flow of molten alloy is directed into the cavity in the molds at this point.

Referring to FIG. 3, which shows the mold segments in open position, each segment has an article forming recess 34 and these two recesses cooperate when the mold segments are placed together to make an article forming cavity. From the article forming cavity in each mold segment to the top of each segment is a growth recess 36 and these recesses cooperate to form a growth zone cavity for a purpose which will appear. At the bottom of each mold segment is also a growth recess 38 extending from the article forming recess to the bottom of the mold segment. These opposed recesses form a growth cavity when the mold segments are in closed position. The growth cavities formed by the recesses 36 and 38 are in vertical alignment with one another and together form a smooth transition from the top of one article cavity to the bottom of the article cavity in the next-above mold.

From this figure it will be apparent that there is a continuous casting cavity extending through the series of molds when they are held in operative position by the conveyor belts. These molds as shown provide for the growth of columnar grains within the molds and the purpose of the growth zone cavities is to provide a gradually widening passage from the tip 40 of each article cavity, the latter being shown as a cavity for casting a turbine blade to the base 42 of the next adjacent article forming cavity, the latter being the root of the blade. In this way a smooth transition takes place from the airfoil shape at the tip 40 of one cavity to the generally rectangular blade root shape of the next adjacent cavity.

The device is intended for use on high temperature superalloys of the type particularly adapted for use in gas turbine engines and may be in general the type of alloy described in the VerSnyder Pat. No. 3,260,505 and the Piearcey Pat. No. 3,494,709. Alternatively, the apparatus can as well be used in the eutectic type of alloy described, for example, in the Gell Pat. No. 3,567,526.

In adapting the molds to the manufacture of single crystal articles rather than to the manufacture of columnar-grained articles as in FIG. 3, it may be advantageous to form the mold segments 24a and 24b with a different form of connection between adjacent molds. As shown in FIG. 4, the top of the article recess 34' in each mold segment has an upwardly converging extension 44 terminating in a relatively small vertical groove 46 extending to the topof the mold segment. This slot 46 communicates at the bottom of the next-above mold with a corresponding slot 48 which, shortly above the bottom of the mold segment, enters an upwardly diverging portion 50 communicating with the base of the root 42' of the article recess. As in FIG. 3, when the mold segments 24a and 24b are placed in juxtaposition for forming the mold cavity, the cooperating grooves 46 and 48 and the expanding portion 50 form a growth zone or crystal selector which make sure that the single crystal grown in one of the mold cavities is continued into the next-above cavity so that the cast alloy does not lose its single crystal character during the operation of the apparatus. Instead of the straight vertical grooves 46 and 48, a slantwise passage of relatively small cross section as in the Piearcey patent may be substituted in assuring the selection or the maintenance of a single crystal as described in that patent.

In operation of the apparatus, the mold segments are carried slowly over the top rolls 30 by the conveyor belts thereon and these mold segments are preheated at the same time by suitable preheating elements 52 located, for example, within the rolls 30. These preheating elements serve to raise the temperature of the mold segments to a temperature somewhat above the melting temperature of the alloy preferably about 2,800, or about 300 above the melting point. As the mold segments continue their movement over these rolls and start a downward movement between the two rolls, the mold segments are brought together as will be apparent thereby forming the continuous casting cavity above described with respect to FIG. 3 or FIG. 4. Continued downward movement of the cooperating mold segments now in closed position permits the flow of molten alloy from the filling spout 16 into the cavity so that the mold cavities of the successive molds are filled with molten alloy.

Directly below the rolls 30, the assembled molds carried by the conveyor belts are surrounded by suitable heating means preferably in the form of one or more induction heating susceptors 54 and these susceptors serve to maintain the temperature of the molds and the alloy therein at a superheat preferably about 300 above the melting temperature of the alloy. Obviously, these susceptors are heated by suitable induction coils surrounding the susceptors as described by way of example in the Piearcey patent.

As the filled and now superheated molds and alloy therein continue their downward movement, they pass into a solidifying zone established by cooperating chill plates 56 located closely adjacent to the molds and preferably, as shown in FIG. 2, in such a way as completely to surround the molds. The effect of these chill plates is to remove heat rapidly from the molds as they move downwardly and by reason of the downward movement of the molds to cause the removal of heat to occur first at the bottom of each of the mold cavities and then continue graduallly from bottom to top of each mold. In this way the directional solidification as described in either of VerSnyder or Piearcey is caused to take place and the result is either the columnar grain cast articles made by the molds of the type shown in FIG. 3 or a single crystal cast article as made by the mold of FIG. 4.

It is desirable to have as steep a thermal gradient between the high temperature zone within the susceptor and the cold zone in the space within the chill plates. To this end, the top of the chill plate is preferably located closely adjacent to the bottom of the susceptors 54 and suitable insulating baffles 58 are preferably positioned between the susceptor and the chill plate so that there will be no direct loss of heat therebetween. These baffles may be, if desired, of the type shown and described in the copending application of Barrow, et al., Ser. No. 63,143 filed Aug. 12, 1970, having the same assignee as the present application. The Barrow application describes the importance of the steep thermal gradient existing therein and the manner of obtaining the solidification by the use of a heat release area directly below the hot zone with a downward movement of the mold therethrough.

As each of the molds passes below the region of the chill plates, the alloy therein will have been completely solidified and as the conveyor belts move around the bottom rolls 32 and cause the mold segments to move apart, the cast material in the form of successively cast articles interconnected by the growth zone elements continues its downward movement and is moved out of the vacuum chamber through a sealed opening 60 therein. If desired, suitable mold cleaners 62 may be provided below the rollers 32 in a position for cleaning the recesses in the several mold segments as they pass the cleaners. These cleaners may be of any suitable type as, for example, vibratory cleaners of well-known construction.

The continuous casting operation above described may be started in the form either of columnar grained cast material or single crystal castings by positioning a properly oriented seed grain or single crystal section of a casting or a ceramic plug in one of the mold segments at the top of the device at a point where it will be located in a closed mold just prior to the pouring of alloy therein. This crystal will have the appropriate orientation of crystalline growth therein and will be formed of the same material of which the finished casting is to be made, that is to say either columnar grain or single crystal. The positioning of this crystal will be such that a portion of it will not be melted as the molds pass downwardly through the graphite susceptor so that, as it reaches the solidification area, it will form a nucleus from which the crystalline structure within the communicating mold cavities will grow. Once the desired type of crystalline growth is obtained at the start of the operation, it will continue through a continuous operation of the apparatus so long as molten material is supplied to the molds as desired. Obviously, once the finished casting is outside of the vacuum chamber, the cast articles, the turbine blades, vanes, airfoils or the like may be removed from the portion of the casting that extends between and interconnects the successive cast articles.

I claim:

1. Apparatus for continuous casting of columnar grained articles including:

a plurality of molds,

means for heating said molds prior to filling the molds,

means for filling the molds with molten alloy,

means operative subsequent to the filling of the molds and located in surrounding relation to the filled molds, after they are filled for further heating the filled molds to maintain a temperature above the melting point of the alloy,

means closely adjacent to said further heating means for rapidly cooling the molds, and

means for advancing said molds successively past said heating means, said filling means, said further heating means, and said cooling means.

2. Apparatus as in claim 1 in which the advancing means is in the form of a conveyor device.

3. Apparatus as in claim 1 in which the further heating means is an induction heating device including a susceptor through which the molds are advanced.

4. Apparatus as in claim 1 including means for melting the alloy prior to filling the mold and a vacuum chamber in which the apparatus in enclosed.

5. Apparatus as in claim 2 in which each mold is in segments and the conveyor device moves the segments together for receiving the molten alloy and also moves the segments apart after the alloy is solidified for removal of the casting from the molds;

6. Apparatus as in claim 5 in which the mold segments are carried on opposed conveyors and are held in operative relation by said conveyors with the successive molds in close relation to one another for continuous filling.

7. Apparatus as in claim 1 in which each mold has an article forming cavity therein and passages from said cavity to top and bottom surfaces of the mold, said passages in adjacent molds being in vertical alignment with the article cavity and forming an interconnection between the article cavities in successive molds, thereby establishing a continuous passage through the several molds for the formation of a continuous casting, the passage from the cavity to the bottom surface being a crystalline growth passage to determine the crystalline structure of the cast article in the article cavity.

8. Apparatus for continuous casting of columnar grained articles including:

a plurality of molds each made up of separate cooperative segments,

a pair of conveyors including top opposing rollers and a pair of belts passing over said rollers, each belt supporting one set of the segments of successive molds, said belts being vertically positioned to bring the cooperating segments of each mold successively into cooperative relation with one another with successive molds also in endwise contact,

means adjacent to the top of the pair of belts for heating the mold segments before being brought into cooperative relation,

means adjacent the top of the pair of belts for filling each mold successively as the mold segments are placed in cooperative relation,

means surrounding the assembled molds below the pair of rollers and below the filling means for additionally heating the molds and the alloy therein to maintain a temperature above the melting point of the alloy, and

means directly below the additional heating means and in surrounding relation to the molds for rapidly cooling the filledmolds as they are moved downward by the conveyor belts for causing effectively an upward directional solidification of the alloy in the molds.

9. Apparatus as in claim 8 including heat insulating baffles positioned between the bottom of the additional heating means and the top of the cooling means to increase the thermal gradients in the mold.

10. Apparatus as in claim 8 in which each mold has an article forming cavity therein and passages from said cavity to top and bottom of the mold in vertical alignment with the cavity, said passages in adjacent molds being in alignment to form an interconnection between the article cavities in successive molds, thereby making a continuous passage through the molds for the formation of a continuous casting the passage from the cavity to the bottom of each mold being a crystal growth controlling passage. 11. Apparatus as in claim 8 in which the conveyor belts are so positioned as to separate the mold segments below the cooling means for removal of the cast articles, and

means for cleaning the mold segments on the belts between the point of article removal and the first mold heating means. 12. Apparatus as in claim 8 including means above the mold filling means for continuously melting the alloy for maintaining a supply of molten alloy in said filling means. 

1. Apparatus for continuous casting of columnar grained articles including: a plurality of molds, means for heating said molds prior to filling the molds, means for filling the molds with molten alloy, means operative subsequent to the filling of the molds and located in surrounding relation to the filled molds, after they are filled for further heating the filled molds to maintain a temperature above the melting point of the alloy, means closely adjacent to said further heating means for rapidly cooling the molds, and means for advancing said molds successively past said heating means, said filling means, said further heating means, and said cooling means.
 2. Apparatus as in claim 1 in which the advancing means is in the form of a conveyor device.
 3. Apparatus as in claim 1 in which the further heating means is an induction heating device including a susceptor through which the molds are advanced.
 4. Apparatus as in claim 1 including means for melting the alloy prior to filling the mold and a vacuum chamber in which the apparatus in enclosed.
 5. Apparatus as in claim 2 in which each mold is in segments and the conveyor device moves the segments together for receiving the molten alloy and also moves the segments apart after the alloy is solidified for removal of the casting from the molds.
 6. Apparatus as in claim 5 in which the mold segments are carried on opposed conveyors and are held in operative relation by said conveyors with the successive molds in close relation to one another for continuous filling.
 7. Apparatus as in claim 1 in which each mold has an article forming cavity therein and passages from said cavity to top and bottom surfaces of the mold, said passages in adjacent molds being in vertical alignment with the article cavity and forming an interconnection between the article cavities in successive molds, thereby establishing a continuous passage through the several molds for the formation of a continuous casting, the passage from the cavity to the bottom surface being a crystalline growth passage to determine the crystalline structure of the cast article in the article cavity.
 8. Apparatus for continuous casting of columnar grained articles including: a plurality of molds each made up of separate cooperative segments, a pair of conveyors including top opposing rollers and a pair of belts passing over said rollers, each belt supporting one set of the segments of successive molds, said belts being vertically positioned to bring the cooperating segments of each mold successively into cooperative relation with one another with successive molds also in endwise contact, means adjacent to the top of the pair of belts for heating the mold segments before being brought into cooperative relation, means adjacent the top of the pair of belts for filling each mold successively as the mold segments are placed in cooperative relation, means surrounding the assembled molds below the pair of rollers and below the filling means for additionally heating the molds and the alloy therein to maintain a temperature above the melting point of the alloy, and means directly below the additional heating means and in surrounding relation to the molds for rapidly cooling the filled molds as they are moved downward by the conveyor belts for causing effectively an upward directional solidification of the alloy in the molds.
 9. Apparatus as in claim 8 including heat insulating baffles positioned between the bottom of the additional heating means and the top of the cooling means to increase the thermal gradients in the mold.
 10. Apparatus as in claim 8 in which each mold has an article forming cavity therein and passages from said cavity to top and bottom of the mold in vertical alignment with the cavity, said passages in adjacent molds being in alignment to form an interconnection between the article cavities in successive molds, thereby making a continuous passage through the molds for the formation of a continuous casting the passage from the cavity to the bottom of each mold being a crystal growth controlling passage.
 11. Apparatus as in claim 8 in which the conveyor belts are so positioned as to separate the mold segments below the cooling means for removal of the cast articles, and means for cleaning the mold segments on the belts between the point of article removal and the first mold heating means.
 12. Apparatus as in claim 8 including means above the mold filling means for continuously melting the alloy for maintaining a supply of molten alloy in said filling means. 